Domestic appliance



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DOMESTIC APPLIANCE Original Filed Nov. 5, 1939 e Sheets-Sheet 9 Patented June 19, 1951 UNITED STATES PATENT OFFICE DOMESTIC APPLIANCE Francis H. McCormick, Oakwood, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware 4 Claims. 1

This invention relates to a domestic appliance and more particularly to heating arrangements in electric stoves.

This application is a division of my copending application S. N. 302,728 filed November 3, 1939, now Patent 2,442,900, which in turn is a continuation in part of application S. N. 208,143, now abandoned, for Domestic Appliance, filed May 16, 1938.

It has been found that a more uniform temperature will be attained in an oven by supplying the major portion of the heat at the bottom and a small amount of evenly distributed heat at the top of the oven. The space within the oven is made more usable by providing the broiling heater at the top of the oven. If separate heaters are provided in the top of the oven for broiling and for baking the heaters will interfere to prevent either heater from providing the desired uniform distribution.

It is an object of my invention to provide an arrangement for a heater in the upper portion of the oven which will cause the heater to supply heat uniformly at a sumcient rate for broiling when desired or at a much lesser rate when it is desired to use the oven for baking.

I have found that the inner portion of the electric surface heaters tends to become much warmer than the outside portion of such heaters, even though it has been customary to provide the heat uniformly over the surface of the heaters. One reason for this is that the outer portions of such heaters are exposed to relatively cool air as well as cooler portions of the range adjacent the heaters. Convection currents at the outer edges of the heaters carry away heat from the outer portions of the surface heaters with considerable rapidity. The inner portions of the heaters are separated from the convection currents of cool air as well as cooler portions of the range adjacent the heaters by the outer portions of the heaters, and the hot air rising from the outer portions of the heaters. This condition is frequently made worse by reason of the fact that cooking utensils often have concave bottoms and thus tend to make contact only on the outside of the heater and ordinarily remain out of contact on the inside or center. This causes most of the heat to be conducted directly from the heater to the utensil or to the outer portion thereof, while the inner portion is forced to employ some less eflicient manner of heat transmission.

It is therefore an object of my invention to provide an electric surface heater in which the heating intensity increases from the inner portions to the outer portions of the surface heater.

It is another object of my invention to provide an electric surface heater formed of a plurality of concentric rings in which the outer ring has a greater density of wattage per square inch than the inner ring.

The problem of providing uniform heat distribution for a wide variety of food loads in an oven is perpetual and continuing. Apparently there is no perfect solution to the problem; but improvements are always possible and desirable. It is customary to place the main heating unit in the bottom of the oven. This, however, has a tendency to make the portion of the oven immediately above the heating unit too hot. Various forms of baffles or heat shields over the lower heating unit have been tried but I find these forms are rather ineffective and tend to trap the heat in the bottom of the oven.

It is an object of my invention to provide a heating arrangement for an electric oven which will provide a more even distribution of heat and particularly will prevent the burning of the bottom food being baked on the lower shelf in the oven.

It is another object of my invention to provide an improved baflie arrangement for the heater in the bottom of the oven which will shield the lower shelves from radiant heat and provide a gentle evenly distributed circulation of hot air in the oven but which will avoid the trapping of heat beneath the bafile.

It has been found that in order to obtain uniform temperature distribution over an area adjacent to a heating unit of radiant type, it is desirable to reduce the heat intensity adjacent the center of the heating unit and to increase the heat intensity of the edge portions of the heating unit. This is true for baking and broiling as well as surface heating units.

It is therefore another object of my invention to provide an improved arrangement of the heating means in the bottom and top of the oven to increase heat intensity at the edges of the heating means and especially at the front and rear edges in order to obtain more uniform temperature distribution.

It is still another object of my invention to provide a heating means with an improved support for the insulators of the electric resistance means.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a perspective view of an electric stove embodying my invention;

Fig. 2 is a fragmentary rear view of an electric stove embodying my invention;

Fig. 3 is a. complete wiring diagram for an electric stove shown in Figs. 1 and 2;

Fig. 4 is a wiring diagram of the oven heating system together with its control switch shown in off position;

Fig. 5 is a wiring diagram of the oven heating system with the control system shown in low heat position;

Fig. 6 is a wiring diagram of the oven heating system with the control switch shown in baking position;

Fig. 7 is a wiring diagram of an oven heating system with the control switch shown in broiling position;

Fig. 8 is a vertical transverse sectional view through the oven, both heating elements and the baffle;

Fig. 9 is an enlarged sectional view of a portion of the lower heating means shown in Fig. 8;

Fig. 10 is a sectional View through one of the insulators taken along the lines l0-l E1 of Fig. 11;

Fig. 11 is a sectional view of a portion of the heating means shown in Fig. 9 taken along the lines lll| of Fig. 9;

Fig. 12 is a plan View of one of the heating units for the oven, the upper and lower heating units of which may be made identical;

Fig. 13 is a modified form of the heating means shown in Fig. 12, made so as to provide a greater amount of heat at all of the edges;

Figs. 14 to 19 inclusive are diagrammatic representations of modified forms of wiring construction;

Fig; 20 is an enlarged view of a portion of Fig. l; and

Fig. 21' is a vertical cross-sectional view taken along the center of the cable channel 34.

Briefly, I have shown an improved electric stove or range which is simple and desirable in construction. It is provided with surface heaters having two concentric heater rings and the outer heating ring has a sufficiently greater heating capacity to provide a greater heating effect per source inch than the inner ring. Preferably the outer ring has at least twice the heating energy of the inner ring. For high heating both the rings are energized to their full capacity, while for medium heat the inner ring only is energized at only one-half voltage and provides a heating effect equal to about one-half of the full effect of the inner ring and about one-fourth of the full heating effect of the outer ring. This heating arrangement provides a greater heating effect upon the outside ring where the cooking utensils normally contact and it also provides a better selection of heating rates for normal cooking require ments. I have found that the heating capacity for medium heat should be considerably less than one-half the high heating rate and that the low heating rate should be about one-half the medium heating rate.

I have provided two identical heating units in the top and bottom of the oven and I provide an evenizer baflie over the top of the lower heating unit to make the heating of the oven much more uniform. The upper heater I use at maximum capacity for broiling, while for baking I use the lower heater at maximum capacity at the full voltage'and upper heater I use at one-half voltage and, in addition, connect the upper heater in series with an external resistance which further reduces the actual voltage upon the upper heater. By this arrangement I can use an evenly distributed heater in the upper portion for both broiling and baking in order to get uniform heat distribution for either broilingfor baking. I also provide a preheating arrangement by which both upper and lower heaters are operated at full voltage and maximum capacity.

Referring now to the drawings and more particularly to Fig. 1 there is shown an electric range including a range shell 20, preferably coated with porcelain inside and out, which is provided with a cooking top 22 having an integral back panel 24, all of which is coated with porcelain on both sides. Ihe top is provided with four surface heaters 26, each provided with an outer heating ring 28 and an inner heating ring 33. These heating rings form the surface heaters and are made of different sizes and different heating rings.

For example, the inner ring may have an outer diameter of 4 /2 and an inner diameter of 2 and an upper surface area of about 12 square inches. Preferably it has a rate of 400 watts at full voltage giving it a heating density of about 33 watts per square inch. The outer ring preferably has an outer diameter of about 6 /2 and an inner diameter of about 4 4 providing an upper surface area of about 1'7 square inches. Preferably this outer ring has a heating ring of about 800 watts providing a heat density of about 50 watts per square inch. This provides about 59% greater heating density in the outer ring than in the inner ring. This counteracts the tendency of surface heaters to get much hotter on the inner portions than the outer portions. I find that cooking utensils often have concave bottoms causing them to contact upon the outside ring and usually fail to make contact with the inside ring. Thus the heat will be removed from the outside ring much more easily than from the inside ring and the greater heating density provided by the outside ring will therefore compensate for its greater rate of heat transfer to keep both rings at about the same temperature.

If desired, the surface heaters may have more than two concentric heatin rings with the inner rin having the least heat intensity and the outer ring having the greatest heat intensity. In such a surface heater, the intermediate heating rings preferably have an intensity intermediate the heat intensity of the inner and outer rings. If there are more than one intermediate ring their heat intensity may be graduated so that the heat intensity of the heaters increases progressively from the inner ring to the outer ring. Other types of surface heaters may also be made so as to provide greater heat intensity upon the outer edges thereof than upon the inner portions thereof. For example, surface heaters of the spiral coil type may have their coils widely spaced in their inner portion and closely spaced in their outer portions to provide greater heat intensity in the outer portions. The spacing of such coils preferably progressively decreases from the inner portions to the outer portion to provide a progressively increasing heat intensity.

The bottom of the surface heaters 26 are separated from their switches by a switch shield 32 located beneath the top cover 22 and extending generally downwardly at an angle from its front edge. A U-sha'ped channel 34 is connected to the shield and conducts the necessary wiring from the surface heaters to the service heater switches 84, 86, 36 and 88. These surface heater 5. switches form a part of a switch channel assembly which includes the switch channel 38 which is fastened by screws at its opposite ends to the front portions of the range shell 20. The switch channel has the surface heater switches 84, 86, 36 and 88 fastened to its rear face and the operating shafts of the switch extend forwardly through the switch channel so that they may be provided with switch handles after a switch panel is placed oved the switch panel assembly. The switch channel assembly is also provided with a fuse and fuse receptacle member 40. The wiring from the switch channel assembly is grouped together in sort of a flexible conduit 42 which extends rearwardly through a channel 44 located immediately beneath the cooking top 22 and extending from the front to the back of the range.

Directly beneath the surface heating units 26 is a large warming drawer 46 and beneath this large drawer 46 is an electric heater called a warming unit 48 by which the large drawer may be heated for keeping food which has already been prepared at a desirable temperature or it may be used to warm dishes prior to serving of a meal.

The walls of the oven proper are provided by an oven shell 50 which fits into the front of the range shell 20. The oven shell 50 is surround-- ed with insulation and through its rear wall extend the plug receptacle 52 and 54. The upper oven heating unit 55 plugs directly into the upper receptacle 52 while the lower oven heating unit 58 plugs into the lower receptacle 54. These upper and lower oven heating units are identical except for the fact that the lower heating unit is provided with an evenizer baffie 60 for the purpose of balancing the distribution of heat through the oven. Each of the oven heater units are of the open coil type and are designed to provide a uniform heat distribution over their entire area. They have a rating of 2000 watts at full voltage.

The oven heating units are controlled by an oven switch 62 having a knob located upon the front face of back panel 24 and the remainder of the mechanism located upon the rear of the back panel 24. As will be further explained in connection with Figs. 4 to 7 this switch provides an off position, a preheat position, in which both heaters are energized by full voltage to give rapid heating, and a bake position in which the lower heater is operated at full voltage and the upper heater is connected in series with the resistance and the two are operated at one-half voltage in order to provide a small evenly distributed amount of heat at the top of the oven to provide uniform heating for baking purposes. A broiling position is also provided in which the upper oven heat unit is operated alone for broiling purposes.

At one side of the oven switch 62 is the oven temperature control 64 which in reality is a thermostat which operates a set of switch contacts to control the supply of current to the oven heating units. At the side of the oven temperature control 64 there is provided a timer clock 66 which may be used to start and stop the energization of the oven heating units at any particular set time. At the side of the clock 66 is a time signal 68 which may be set to ring a bell at any particular time desired. On the other side of the oven switch 62 is an oven vent I which permits air, odors and vapors to escape from the oven. At the side of this vent I0 is a warmer switch I2 beneath which is a signal light I4 which is lighted whenever the upper unit is in operation. Below the signal light I4 is an appliance receptacle 16 which may be used as an outlet for an electric teakettle or 'percolator or the like.

The external resistance I8 for use with the upper oven heating unit 56 during baking operations is located upon the back of the range and like the other electrical parts is connected to the line terminal block 80 which is located adjacent the bottom of the range to which the supply electric conductors are connected. Preferably the range operates upon a three-wire 115-120, 230-240 volt distribution system. The electrical connections shown in Fig. 2 at the rear of the range are concealed by the rear cover 82 of the range. Referring now more particularly to Fig. 3 which shows the wiring system of the range, the line terminal block 80 is shown connected to the surface heater switches 84, 80, 30 and 88. The connection between these switches and the line terminal block 80 is made by the conductors 42 which pass through the channel 44 provided for them. The switch 84 is connected to the left front surface heater 25 which includes the outer ring-shaped heating member 28 and the inner ring-shaped heating member 30. The switch 84 includes a knob 94 provided with a pointer 96. Four positions ofi, high, medium and low are indicated upon the switch panel.

The knob 9a is connected to a shaft 98 provided with cams I02, I04 and I06. The cam I02 operates the contact I08 which makes engagement with the stationary contact I I0 for supplying current to a connection which connects with one end of each of the heating members 28 and 30. The other end of the heating member 30 is connected to the stationary contact II2 which is adapted to be contacted by the movable contact I I4, which in turn is connected to the middle wire of the terminal block. The other end of the heater 28 is connected to a double stationary contact H6 having a contact H8 adapted to be engag-ed by the movable contact I20 which is connected to one of the outside conductors, while the second contact I22 is adapted to make contact with the movable contact II4 connected to the middle wire.

The other switches are connected to the left rear, right rear, and right front surface units in the same manner as is the switch 84. However, the switch 84 is shown in the off position, with the contact I08 away from the contact H0, and the contact II4 away from the contact II2. In this position, since only one conductor is connected to the supply line, no current can flow through any of the heaters.

When the knob 94 of the switch 84 is turned to the high position, the cam I02 will be turned so that its point of contact with the contact I08 will be changed from its high portion to its low portion. This will permit contact I08 to make contact with the contact H0. The cam I04 will also be rotated but the contact II4 will remain upon the high portion of the cam. The cam I06 will also move one-fourth turn in a. clockwise direction so that the contact of the cam with the contact I20 will be changed from the high portion of the cam to the low portion of the cam. This will cause the contact I20 to engage the contact H8. Thus when the switch 84 is turned to the high position, the current from one of the outside lines will flow through the contacts I20 and H8 to the heater 28. Current from the middle supply line will flow through the contacts H4 and II 2 to the heater 60. Current from the other outside supply line will flow through the contacts I08 and H to both the heater 28 and 30. Thus the current flowing through the outside ring heater 28 .will flow from one outside supply line to the other while the current flowing through the inner heater 30 will flow from the middle supply line to one of the outside supply lines. Thus the outside heater 28 will be supplied with the maximum voltage for which it is designed, namely, 230-240 volts, whilethe inner ring heater 30 will be supplied with its maximum voltage namely 115 to 120 volts. The switch 86 is shown in the high position.

When the knob 84 is turned to the medium position the contacts I08 and III} remain closed and the contact I M remains in engagement with the contact I I2. However, the contact I is again moved out of engagement with the contact I I8 so that no current can flow through the outside ring heater 28. Full voltage, however, is applied to the inner ring heater 30. The switch 36 is shown in the medium position.

In the low position, the contact I08 remains in contact with contact H8, but the contact H4 is moved out of engagement with the contact I I2 and into engagement with the contact I22, because in this position the low portion of the cam I04 makes contact with the contact I I4. In this low position, the contact I20 remains out of contact with the contact I I8. Thus, current from the middle conductor of the three-wire system passes through the contacts H4 and I22, which forms a portion of the double contact member H6, to the outer ring heating member 28, from which the current flows through the contacts I I0 and I68 to one of the outside conductors of the three-wire system. Thus when the switch 84 is in this position only one-half full voltage is applied to the outer ring heater 26 and only onefourth the full heat rating is obtained from the heater 28. The switch 88 is shown in the low position.

Also connected to the three-wire conductors extending from the line terminal block 80 is the warmer unit 48 which is controlled by the warmer unit switch 12. The conductors to the warmer unit 48 are shown as entering an aperture I26 in the rear wall of the range in Fig. 2 and make connection with the warmer unit 48 as shown beneath the large drawer 46 in Fig. 1. The warmer unit is connected to the middle connection and one of the outside connections of the line terminal block 88 so that the warmer unit operates on 115-120 volts. The oven temperature control 64 includes the double contacts I28 connected by conductors I30 to the timer clock 86 which in turn connects to the two outside conductors connecting to the line terminal block 80. The double switch contacts I28 are connected by conductors to the binding posts I32 and I34 of the oven switch 62. The oven switch 62 is provided with a third binding post I86 connected to the external resistance 18 which in turn is connected directly to the middle conductor connected to the terminal block 86.

The upper left front and the upper right rear binding posts I88 and I40 of the oven switch 62 are connected to the terminal 54 which connects to the lower oven heating unit 58. The left rear and right front binding posts I42 and I44 of the oven switch 62 are connected to the upper terminal 52 to which is connected the upper oven heating unit 56. The signal light 14 is connected to the conductor which is connected to the binding post I42 and is also connected to one of the terminals of the appliance receptacle 16 which in turn is connected to the middle conductor connected to the line terminal block 80. The other conductor of the appliance receptacle is connected to a fuse I46 which in turn is connected to one of the outside conductors connected to the line terminal block 80.

Referring now more particularly to Figs. 4 to '1 inclusive, there is shown the oven switch I02 in its four positions connected diagrammatically to the upper and lower oven heating units 56 and 58. In Fig. 4 the oven switch is shown in the off position as indicated by its control knob I50. The knob I50 is connected to one end of a cam shaft I52 which is provided with cams I54, I56, I58, I60 and I62 arranged upon the shaft I52 in order. The cam I54 is contacted by the contact member I64 which is adapted to make contact with the stationary contact I66 connected to the external resistance 18. The high portion of the cam I54 is in contact with the contact I64 at all times except when the knob I50 is turned to bake position as is shown in Fig. 6, at which time the contact I64 will be engaged with the low portion of the cam I50 to permit the contacts 44 and I66 to close.

The cam I56, which is next in line, is engaged by the contact I68 which is adapted to make contact with the stationary contact I18 forming a part of a contact bar I12 which it shares with the stationary contact I14. The high portion of cam I56 remains in engagement with the contact I68 keeping it in open position in the oiT and high positions, but in the preheat and baking positions contact I68 is engaged with the low portion of the cam I56 so that it makes contact with the stationary contact I10. The contact I68 is on the same side of the shaft as the contact I16 which is operated by the cam I60. When the knob I50 is turned to the preheat and bake positions the contact I16 is in contact with the low portions of the cam I60 so that the contact I16 is in engagement with the contact I14 upon the contact bar I12 at the same time when the contact I68 is in contact with contact I10 upon the other end of the contact bar I12. However, in the broil position the contact I16 is also in engagement with the low portion of the cam I60 so that it remains in engagement with the contact bar I12 while the contact I68 is moved away from contact bar I12 by the high portion of its cam I56.

Upon-the other side of the cam shaft I52 is another contact bar I provide-d with a stationary contact I82 adapted to make contact with a movable contact I84 which is operated by the cam I58. The other stationary contact I80, upon the contact bar I80 is adapted to be contacted by the movable contact I 88 which is operated by the cam I62. In the preheat position the low portion of the cams I58 and I62 are in contact with the movable contacts I84 and I 88 so that both of these contacts are in conducting relation with the contact bar I80 which is connected to one outer conductor connected to the line terminal block. When the knob I50 is turned to the bake position, the cam I58 has its high portion in engagement with the movable contact I84 thus disengaging it from its stationary contact I82 upon the contact bar I80. The cam I62, however, has its low portion in engagement with the movable contacts -I88 so that it remains in contact with its stationary contact I86. In the broil position of the knob I 50, the situation is reversed and the low portion of the cam I58 engages the movable contact I84 permitting it to contact the stationary contact I82 while the high portion of the cam I62 is engageable with the movable contact I88 to separate it from its stationary contact I86.

Thus it will be seen in the off position all of the contacts are separated from their cooperating contacts to prevent any energization of the heaters. In the preheat position one of the outside conductors connecting to the line terminal block is connected through contact bar I12 with both the movable contacts I68 and H6 to supply electric energy at full voltage to both the upper and lower heating units 56 and 58. The upper oven heating unit 58 is also connected through a common conductor I80 to the movable contact I84 and through the common conductor bar I88 to the other side of the three-wire system connected to the line terminal block. The lower oven heating unit 58 is also connected to the movable contact I88 which engages the common contact bar I88 connected to the other outside conductor of the three-wire conducting system connected to the line terminal block 88. Thus it will be seen that in the preheat position the heating units have one end connected to the common contact bar II2 while the other end is connected to the common contact bar I08.

In the bake position shown in Fig. 6 one of the outside conductors is connected to the common contact bar I'IZ and through this bar to the movable conductor I88 and to the lower oven heating unit 58 which in turn is connected through the movable conductor I88 to the other common contact bar I88. In this control posi tion the common contact bar I12 is also contacted by the movable contact I18 which connects to the upper oven heating unit 56 which in turn is connected to the common conductor I90 which is connected to the movable contact I64 which in turn engages the contact I66 connected to the external resistance I8 to apply the 115-120 volts to the upper oven heating unit 58 and the resistance I8 so that the heat output of the upper oven heating unit will be reduced. to about 250 watts.

In the broil position shown in Fig. '7, common contact bar H2 is engaged by the movable contact I'I6 which permits current to how to the upper oven heating unit 56 which is connected to the common conductor I80 and to the movable conductor I84 which contacts the common contact bar 88 so that in this position full voltage is applied to the upper oven heat unit 56 for broiling purposes. In this position all the other contacts are in open position.

By this particular heating arrangement for the oven, the top heating coils for both broi ing and baking are evenly distributed over the top of the oven so that the heat at the top of the oven is evenly distributed over the entire top of the oven for both broiling and baking. This particular arrangement avoids using separate sections of the upper heating unit for broiling and baking purposes. Obviously this particular arrangement provides improved broiling and baking conditions.

I have provided two similar heating units in the top and bottom or" the oven and I provide a baffle over the top of the lower heating unit to shield the lower shelves from the radiant heat and to provide a gentle circulation of the warm air in the oven to make the heating of the oven 10 the flanged opening in the bailie.

40 receptacle 54.

10 much more uniform. This baifle is of a peculiar shape and is inclined upwardly from its centerportion toward its outer edges. It is provided with a long downwardly flanged opening ex- 5 tending generally from front to rear, in order to provide a passage through which air from the upper portion of the oven may readily enter the space beneath the bafiie. The lower heating unit is entirely covered by the baiile and surrounds The upper heating unit I use at a maximum capacity for broiling, while for baking I use the lower heating unit at maximum capacity at the full voltage, and the upper heating unit I use at one-half voltage and in addition connect the upper heating unit in series with an external resistance which further reduces the actual voltage applied to the upper heating unit. The heating units are provided with an arrangement creating a greater heat intensity at their front and rear edges. By this arrangement I provide an even distribution of heat in the upper portion of the oven for either broiling or baking. I also provide a heating arrangement by which both upper and lower heaters are operated at full voltage and operated at maximum capacity for rapid heating.

I While the low intensity, distributed heat in the top of the oven is a great aid in providing uniform distribution of heat, it is of primary importance that the lower oven heating unit be provided with properly distributed heat and be bafiled in the most eflicient manner. Referring now more particularly to Figs. 8 to 13, the lower 'heating element is shown as formed generally of oven shell for holding the lower heating unit in place.

Extending between the front and rear portions of the wire frame members 220 and 224 are the channel members 238 which are formed of sheet steel. These channel members 238 include a web portion 232, upper and lower flanged portions 284 and 236, and these flanged portions have their edges turned inwardly as designated by the reference characters 238 and 240, so as to receive the rectangular insulating blocks 242 which are provided with central apertures 244. These channel members 238 therefore form a slideway for these insulating blocks 242. At uniformly spaced distances each of the channel members is provided with a rectangular opening 248 which is just slightly wider than the insulating block. Each of these flanged openings registers with the opening in its respective insulating block 242. The edges of the openings 246 are pressed inwardly as designated by the reference characters 248 and 258 in order to locate the insulating blocks in place within the confines of the channel members so as to prevent lateral movement and to hold them in alignment with the apertures 246 in the web of the channels 238, the web 232 of the channels 230 are provided. with rectangular notches 252 at each corner thereby leaving the protruding end portions 2.54 and 258 which are bent around the front and rear portions of the upper and lower 1 1 Wire frame members 220 and 224 which are provided with flatted portions or notches 258 in order to hold the channels in position.

The electric heating unit is provided with an electrical resistance heating element in the form ofa coiled resistance wire havin such a resistance as to provide 2000 watts at 235 volts. This coiled resistance wire has its opposite ends connected to the plug 222 and is threaded through the insulating blocks 222. It should be noted that the coiled resistance wire does not extend across from one side of the center to the other except in the front of the heater where a single coil of resistance wire extends from one side to the other in order to connect the two sides in series with each other. It should be noted that the resistance wire is not coiled uniformly but that a single pass adjacent the rear edge of the heater on either side of the plug 222 and designated by the reference characters 230 and 262 is coiled considerably closer together than the portion 266 and 268 of the resistance wire in between the portions 252 and 262 and the portion 264. This last mentioned portion 264 is closely coiled like the portions 260 and 2&2 and extends completely across the heater from one side to the other at its front edge and forms the connecting pass between the two sides of the heater.

The coils of wire are so stretched that the portion of the coil between the portion 250 and the portion 264 has a resistance of about 1.4 ohms and likewise the portion between the closely coiled portion 252 and the closely coiled portion 284 also has a resistance of about 7.4 ohms. The

portion 264 has a resistance of about 5.3 ohms and the portions 263 and 222 each have a resist ance of about 26 ohms. It will therefore be seen that the heat intensity is concentrated at the front and rear edges of the heating unit where the greatest amount of heat is desired in order to obtain substantially uniform temperature conditions throughout the oven. Thus in order to secure the desired distribution of heat intensity, the portions 260, 262 and 26 3 have their coils only about one-half as far apart as the portions 266 and 268 which are located between the closely coiled portions. Thus I provide a distribution wherein about 20% of the heat is provided at the front and substantially the same proportion at the rear edge of the heater and slightly less than 60% or" the heat is provided in between the front and rear edges.

In order to provide a satisfactory distribution of heat from the. lower heating unit 58 I provide the bafile 50 directly above it. This battle is supported by four supports 216 which are fastened to the front and rear edges of the baffle 69 adjacent the corners and extend downwardly and are fastened to the front and rear edges of the upper wire frame member 220. This bafile 65] has its outer edges 212 curled downwardly a small distance providing a reinforcement for its edges and at its center portion it is provided with a deeply flanged aperture 214 which is flanged downwardly a considerable distance very nearly to the level of the coiled resistance wire. The bafile 6B slopes upwardly on either side of the long flanged aperture 21d at a uniform slope of about 5. This bafile provides a means of protecting the food on the lower shelves of the oven from obtaining too much radiant heat from the lower heating unit. Thus this bafile serves as a shield since it completely covers the portions of the heating unit which contain the coiled resistance wire.

It also serves as a means to promote a gentle evenly distributed circulation. runs the uniform slope of the bafile on each side of theflanged aperture 214 produces a circulation of warm air laterally under each side of the baflle and upwardly along the side walls and then to distribute itself through the interior of the oven. The flanged aperture 214 provides a means by which the air when slightly cooled may be returned to the lower heater beneath the baiile. The deep flange of the flanged aperture 214 tends to prevent, to a certain extent, any Warm air from passing upwardly through it instead of passing laterally beyond the side edges of the baiiie. I find that this deeply flanged aperture in the center of the bafile increases the rate of circulation over baffles which have previously been used thereby avoiding the trapping of heat beneath the baiiie, and thus provides a much more even distribution of heat in the oven. This baffle is not only useful with the two unit type of oven shown in the drawings, but may also be used with the single unit type of oven where space is provided for broiling beneath the lower heatin unit.

As mentioned before the upper heating unit 56 is identical to the lower heating unit 58 excepting that it is inverted. It is supported in slideways 21% and 218 provided upon the top wall of the oven, which slideways are similar to the slideways 216 and 218 provided in the bottom. The increased heat intensity at the edges of the upper unit 56 provides much better broiling conditions than prevails in other heating units and also provides better baking conditions. The side walls of the oven are provided with projections 28!] which form supports and guides for the shelves 282. Thus by providing a lower oven heating unit with about 40% of its heating capacity located upon its front and rear edges and by providing this greatly improved form of baths, and also by .providing a properly distributed small amount of heat at the top of the oven I have provided an oven which provides much more uniform heating than has heretofore been accomplished with an arrangement of this type.

In Fig. 12 is shown a modified form of heating unit designated by the reference character 358 which is formed of the upper and lower rectangular wire frame members 326 and 324 which are provided with channel members 33!) extending from front to rear as in the heating unit 58. These channel members are constructed like the channel members of the heating unit 58. The coiled electrical resistance wire is threaded through the insulators supported by the channel members 330 in a fashion like that shown in Fig. 12 for the lower heating units 58.

This coiled resistance wire diners from that shown in Fig. 12 by having closely coiled portions 366 and 362 at the rear edge of the heating unit which extend not only across the rear edge of the heating unit but these closely coiled portions extend to form a loop upon the side of the heating unit. Connected to the closely coiled portions 360 and 362 are the loosely coiled portions 364 and 366 which form loops on the inner portions of the heating unit. These loosely coiled portions are then connected to closely coiled portions 368 and 310 which form loops at the outer edge of the heating unit. The resistance element then continues in alternate loosely coiled and closely coiled portions with the loosely coiled portions forming the inner loops, while the closely coiled portions form the outer loops until the front of the heating unit is reached, where a closely coiled portion 312 is provided which ex- 13 tends entirely across the front of the heating unit and also forms loops at the outer edges of the heating unit.

Thus with this form, the heating unit is provided with closely coiled portions at the front and rear as well as in the loops on the outer edges, while the loops on the inner portions of the heating unit are loosely or widely coiled. This provides a greater amount of heat at all the edges of the heating unit and a lesser amount of heat in the central portions of the heating unit. Thus this form creates more heat at the edges, and in this way provides more uniform temperature distribution which is advantageous for broiling as well as baking. This modified form of heating may be used like the heating unit 58 in either the single or two unit oven. It may be used with a similar bafile 340 provided with a deep downwardly flanged aperture 314. It may also be used as the upper heating unit in connection with a lower heating unit like that of Fig. 12. If desired, a diiferent baflle may be used or a different slope employed such as 10".

From the foregoing description of the oven heating system, it is to be seen that I have provided a system in which upper and lower oven electric resistance heater units are controlled by a unitary manual switch. The upper heater is primarily suitable for broiling purposes when applied to full voltage. The lower electric heater unit is primarily suitable for baking purposes when applied across the full voltage. I connect the heaters to electric supply means in such a manner that the upper heater unit is used alone across the full voltage for broiling purposes, while for baking purposes the upper heater unit is placed across a reduced voltage simultaneously energized with the lower heating unit with the full voltage across the lower unit.

In the foregoing description I have indicated how these oven heating units may be applied to a three-wire circuit; but other modifications are possible with both three-wire and two-wire circuits. Such modifications are diagrammatically indicated in Figs. 14 to 19 inclusive.

In Fig. 14 the upper and 1 wer heating units are shown at 55 and 53. A two-line source of electrical supply is indicated by the wires 41m and 4M. A resistance 4&2 may be placed outside of the oven, and a multiple switch 4% with 5 a single manual control is provided for regulating the energization of'the oven units. The arrangement is such that switching mechanism 493 can disconnect the units 55 and 58 completely from the source of supply, can place both units across the full voltage for preheat, can place the lower unit 58 across the full voltage with the upper unit 55 across a reduced voltage for baking, and can place th upper unit 55 alone across the full voltage for broiling. The switch structure may be of any desired unitary construction such that the necessary contacts can be manipulated from a single handle. This structure, for example may include movable contacts 403a, 4031) interlocked by manipulating arm 4830. When the movable contacts 493a and 4931) are over stationary contacts 434 and 485, the switch is in the off position. At this time the extension 403d of arm 4930 impinges upon, and opens, the switch 49'! thereby disconnecting both sides of the units 56 and 58 from the wires 490 and 46 l.

. When movable contacts 403a and 403?) are moved over stationary contacts 498 and 435, arm extension 4630! is. moved away from switch 491 and switch 401 closes, and the units 56 and 58 are placed across the full voltage in parallel across the wires 4% and 43L In this position of the switch, the units are at the maximum heating capacity and are to be used for preheating the oven. When the movable contacts are placed over the contacts 4!!! and 4, the switch remains closed, the lower unit 58 is across the full voltage, and the upper unit 56 is across a reduced voltage by being placed in series with the resistance 482. In this position the units are suitably energized for baking. When the movable contacts are placed over the contacts M2 and 4K3, the switch 40'! remains closed, and the upper unit alone is placed across the full voltage of the wires 4% and 49 I. This is suitable for broiling.

If desired, an adjustable thermostat having a diaphragm or bellows 4I4 may be connected. to a bulb 415 in the oven in such a manner that the expansion of the bellows M4 by the thermostatic liquid, such as chlorinated diphenyl, opens a switch, such as 431, when the oven reaches a predetermined temperature. By adjusting the impingement or contact screw M5, the operating distance of the bellows may be varied so that the opening temperature of the switch may be varied or selected to suit the user. Also, if desired, an electric clock mechanism may be provided which may be set to close the contacts 65a and 6511 at a predetermined time and to open them at a later predetermined time, thus providing for an automatic baking operation of selected time and duration.

In Fig. 15 the oven units 55 and 58 are connected to a three-wire source including wires 42! 42! and 422. This may be usual three-wire alternating current supply with wire 42! as the neutral wire. The arrangement is such that the switch structure 423 may place both units across the full voltage of wires 420 and 422 for preheat, the lower unit 58 across the full voltage of wires 420 and 422, with the upper unit 56 across the reduced voltage between either of the line wires 42% or 422 and the neutral wire 42! for baking, and the upper unit 56 alone across the full voltage between the wires 42!! and 422 for broiling. For example, when the movable contacts 423a and 4231) are placed over the stationary contacts 424 and 425 by manipulating interlock arm 4230, arm extension 423d impinges on, and opens switch 42 5, so that the units 55 and 58 are completely disconnected from the live wires. When the movable contacts 423a and 4231) are placed over contacts 421 and 428 by means of manipulating interlock arm 4230, switch 425 is closed because extension 42301 is retracted from switch 426. At this time, both units 56 and 58 are placed across the full voltage between wires 429 and 422 thus rendering them suitable for preheating the oven. When the movable contacts 423a and 42321, are placed over contacts 429 and 430i, switch 425 remains closed and the lower unit 58 is placed across the full voltage between line 423 and line 422 with the upper unit across the reduced voltage between the lines 429 and 421. The units are suitably energized for baking in this position. When the movable contacts 423a and 4231) are placed over the contacts 43! and 432, switch 426 remains closed and the upper unit 56 alone is placed across the full voltage of lines 423 and 422 and is suitably energized for broiling. In this modification also, a thermostat 433 is provided similar in function, adjustment etc., to the thermostat shown in Fig.

14. The clock mechanism 66 may also be provided.

In Fig. 16 an arrangement is shown for energizing the units 58 and 58 by means of the twowire source 440 and 44I, utilizing an autotransformer 442. When the switch structure 443 is placed with its movable contacts 443a and 443!) over contacts 444 and 445, the system is in the ad position, with the switch 446 opened by extension 443d of interlock 4430 and with the units 58 and 58 completely disconnected from the electrical supply. When the movable contacts 443a and 4431) are placed over contacts 44'! and 448, the switch 445 is closed, and the units 56 and 58 are placed in parallel across the full voltage of lines 440 and MI and are suitably energized for preheating. When the movable contacts 443a and 4431) are placed over contacts 449 and 459, switch 445 remains closed, lower unit 58 is placed across the full voltage of lines 444 and MI, and the upper unit 56 is placed across a reduced voltage extending from the line 440 to a selected point in the autotransformer 442. The units are suitably energized for baking in this position. If desired, autotransiormer 442 may be made adjustable so that'any desired energization of the upper unit may be obtained. When the movable contacts 443a and 443?) are over contacts and 452, the upper unit 56 alone is placed across the full voltage of the wires 440 and 44! and is suitably energized for broiling. A thermostat 453 may be provided, is similar in construction, adjustment etc., to the thermostat shown in Fig. 14. The clock mechanism 66 may also be provided.

In Fig. 17 the units 56 and 58 are connected to a three-wire source 4%, Mil and 462. In this arrangement a resistance 463 is placed adjacent to the lower unit 58-, and may be built structurally integrally therewith. This resistance may be placed in series with the upper unit 55 across the reduced voltage of 465 and 46! when the switch arrangement about to be described is placed in the bake position. When the movable contacts 434a and 4%417 of the switch structure 464 are placed over the contacts 465 and 45'! by means of the manipulating interlock 4540, the switch 458 is opened by arm extension 464d and the switch structure is in the oiT position completely disconnecting the units 55, 58 and 463 from the electric source of supply. When the movable contacts 464a and 4641) are placed over the contacts 469 and 416, the switch 468 is closed and the units 55 and 58 are placed across the full voltage of lines 468 and 462 and are suitably energized for preheating the oven. When the movable contacts 464a and 4541) are placed over the contacts 4'8! and 412 the lower unit 58 is placed across the full voltage 469 and 452 while the upper unit 56 is placed in series with the resistance 4% across the reduced voltage 463 and 46!. This is suitable energization for baking. When the movable contacts 464a and 4541) are placed over contacts 413 and 474, the upper unit 5% alone is placed across the full voltage of lines 4643 and 482 and is suitably energized for broiling. A thermostat 415 is provided, which may be similar in construction, adjustment etc., to the thermostat shown in Fig. 14. The clock mechanism 65 may also be provided.

In Fig. 18, the units 56 and 58 are connected to a two-wire source 488 and 48!. A resistance 483 may be provided adjacent to, and if 16 I desired integrally built into, unit 5&3. When the movable contacts 484a and 484?) of the switch structure 484 are placed over the contacts 485 and 488 by the manipulating interlock arm 4840, switch 481 is opened by the extension 484d and the arrangement is in the off position with all of the units completely disconnected from the electrical supply. When the movable contacts 484a and 4841) are over contacts 488 and 485, switch 481 is closed and both units 58 and 56 are placed in parallel across the full voltage 434 and 43! and are suitably energized for preheating the oven. When the movable contacts 454a and 4134b are placed over contacts 490 and 4 3i, the lower unit is placed across the full voltage 484 and 44 with the upper unit 56 placed in series with the resistance 483 across 48!] and 481 to impose a reduced voltage on the unit 55. The units are suitably energized for baking in this position. When the movable contacts 484a and 48417 are placed over contacts 492 and 493 the upper unit 5% alone is placed across the full voltage 480 and 48! and is suitably energized for broiling. A thermostat 494 may be provided similar in construction, adjustment etc., to the thermostat shown in Fig. 14. The clock mechanism 66 may also be provided.

In Fig. 19 the units 56 and 58 are connected with the two-wire source 508 and 50!. In this modification a reduced voltage is imposed on the upper unit 56 in the baking position by placing it in series with a portion of the lower unit 58, thus using a portion of the lower unit 58 as a resistance. When the movable contacts 552a and 56-21) of the switch structure 562 are placed over the contacts 593 and 584 by the manipulating interlock e520, the switch 585 is opened by extension 562d and the nuits 55 and 58 are completely disconnected from the source of electrical energy, the switch structure being in the ofif position. When the movable contacts 502a and 54% are placed over contacts 5&6 and Elli, switch 532 is closed, the units 555 and 58 are placed across the full voltage 596 and sea and are suitably energized for preheating the oven. When the movable contacts 5El2a and 5&2?) are placed over contacts 598 and 599, the lower unit 58 is placed across the full voltage 505 and 591 while the upper unit 55 has a reduced voltage imposed on it by placing it in series with a portion of the lower unit 58 across the lines 568 and Bi l. Fhis suitably energizes the units for baking. When the movable contacts 582a and 55222 are placed over contacts 510 and 5 the upper unit 56 alone is placed across the full voltage 568 and 581 and is suitably energized for broiling. A thermostat 552 is provided which is similar in construction, adjustment etc., to the thermostat shown in Fig. 14. The clock mechanism 65 may also be provided.

In the description of Figs. 14, 16, 17 and 18, a two-wire source has been referred to; but it is understood that this two-wire source may be two selected wires of a three or more wire source.

Referring more particularly to Figs. 20 and 21, the switch shield 32 and the U-shaped channel 34 provide a protected conduit under the cover 22 for the wires 84a, 36a, 36a, and 88a leading from the switches 84, 86, 36 and 88 and terminating centrally with respect to the surface heaters 26 so that the wires may be flexibly connected to the respective heaters 26 as indicated. This protects the wires from spillage, and at the same time allows the heaters 26 to be lifted or tilted from the cover 22 a suflicient distance for cleaning the heaters and stove. The U-shaped channel 34 prevents the wires from moving under the surface heaters where they might be damaged by spillage. The unenergized portions of the heaters 26 may be grounded to the channel 34 by wires 26a.

The switch channel 38 may be covered by an enameled plate 3811, through which switch stems 38b extend. Switch knobs 38a are pushed on the stems 38b.

While the forms of embodiment of the invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted as may come within the scope of the claims which follow.

What is claimed is as follows:

1. A domestic electric range comprising a range shell, a cooking top on said shell, electric surface heaters on said top at one side said range arranged about a mutual central point, an electrically heated oven in said shell at opposite side said range from said heaters, a channel underneath said cooking top centrally located on said range between said heaters and oven, a terminal block at the rear of said range, heater switches at the front of said range, wires extending from said terminal block to said switches and to said oven, a second channel extending from said switches and terminating at said mutual central point, and wires connecting said switches and heaters and passing longitudinally through said second channel.

2. A domestic electric range comprising a range shell, a cooking top on said shell, electric surface heaters on said top at one side said range, an electrically heated oven in said shell at opposite side said range from said heaters, switches on said range, an open channel underneath and covered by said cooking top, extending from the proximity of said switches and terminating centrally under said heaters on said range, electric wires from said switches passing longitudinally through said channel and electrically connected to said surface heaters, a terminal block at the rear of said range, a second open channel underneath and covered by said cooking top located to one side of said electric surface heaters and directed toward said terminal block, and elec- 18 tric wires from said switches extending longitudinally through said second channel to said terminal block.

3. A domestic electric range comprising a range shell, a cooking top on said shell, electric surface heaters on said top, an oven underneath said top, a terminal block in the rear of said range, switching and thermostatic controls on said cooking top for said oven, cable connections from said terminal block to said switch and thermostatic controls and from thence to said oven, switches at the front of said range for said electric surface heaters, an open channel underneath and covered by said top extending from the rear of said range to the front of said range, electric wires from said terminal block, longitudinally through said channel to said switches at the front of said range, and wires from said last named switches to said electric surface heaters.

4. A domestic electric range comprising a range shell, a cooking top on said shell, electric surface heaters on said top, an oven underneath said top, a terminal block in the rear of said range, switching and thermostatic controls on said cooking top for said oven, cable connections from said terminal block to said switch and thermostatic controls and from thence to said oven, switches at the front of said range for said electric surface heaters, a channel underneath said top extending from the rear of said range to the front of said range, electric wires from said terminal block, through said channel to said switches at the front of said range, wires from said last named switches to said electric surface heaters, and a second channel under the central portion of said electric surface heaters for supporting said last named wires.

FRANCIS H. McCORMICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,674,995 Rutenber June 26, 1923 2,000,343 Lusher 1- May 7, 1935 2,147,382 Rogers Feb. 14, 1939 2,218,778 Weimer Oct. 22, 1940 2,279,064 Rutenberg Apr. 7, 1942 2,402,787 Stickel June 25, 1946 

